Additive manufacturing techniques and processes generally involve the buildup of one or more materials, e.g., layering, to make a net or near net shape (NNS) object, in contrast to subtractive manufacturing methods. Though “additive manufacturing” is an industry standard term (ASTM F2792), additive manufacturing encompasses various manufacturing and prototyping techniques known under a variety of names, including, e.g., freeform fabrication, 3D printing, rapid prototyping/tooling, etc. Additive manufacturing techniques may be used to fabricate simple or complex components from a wide variety of materials. For example, a freestanding object may be fabricated from a computer-aided design (CAD) model.
A particular type of additive manufacturing is commonly known as 3D printing. One such process, commonly referred to as Fused Deposition Modeling (FDM), or Fused Layer Modeling (FLM), comprises melting a thin layer of thermoplastic material and applying this material in layers to produce a final part. This is commonly accomplished by passing a continuous, thin filament of thermoplastic material through a heated nozzle, or by passing thermoplastic material into an extruder with an attached nozzle, which melts the thermoplastic material into and applies it to the structure being printed, building up the structure. The heated material may be applied to the existing structure in layers, melting and fusing with the existing material to produce a solid finished part.
The filament used in the aforementioned process may be produced, for example, by using a plastic extruder. This plastic extruder includes a steel screw configured to rotate inside of a heated steel barrel. Thermoplastic material in the form of small pellets may be introduced into one end of the rotating screw. Friction from the rotating screw, combined with heat from the barrel may soften the plastic, which may then be forced under pressure through a small round opening in a die that is attached to the front of the extruder barrel. In doing so, a “string” of material may be extruded, after which the extruded “sting” of material may be cooled and coiled up for use in a 3D printer or other additive manufacturing system.
Melting a thin filament of material in order to 3D print an item may be a slow process, which may be suitable for producing relatively small items or a limited number of items. The melted filament approach to 3D printing may be too slow to manufacture large items. However, the fundamental process of 3D printing using molten thermoplastic materials may offer advantages for the manufacture of larger parts or a larger number of items.
A common method of additive manufacturing, or 3D printing, may include forming and extruding a bead of flowable material (e.g., molten thermoplastic), applying the bead of material in a strata of layers to form a facsimile of an article, and machining the facsimile to produce an end product. Such a process may be achieved using an extruder mounted on a computer numeric controlled (CNC) machine with controlled motion along at least the x, y, and z-axes. In some cases, the flowable material, such as, e.g., molten thermoplastic material, may be infused with a reinforcing material (e.g., strands of fiber or a combination of materials) to enhance the material's strength.
The flowable material, while generally hot and pliable, may be deposited upon a substrate (e.g., a mold), pressed down, or otherwise flattened to some extent, and leveled to a consistent thickness, preferably by means of a tangentially compensated roller mechanism. The compression roller may be mounted in or on a rotatable carriage, which may be operable to maintain the roller in an orientation tangential, e.g., perpendicular, to the deposited material (e.g., bead or beads). In some embodiments, the compression roller may be smooth and/or solid. The flattening process may aid in fusing a new layer of the flowable material to the previously deposited layer of the flowable material. The deposition process may be repeated so that successive layers of flowable material are deposited upon an existing layer to build up and manufacture a desired component structure. In some instances, an oscillating plate may be used to flatten the bead of flowable material to a desired thickness; thus, effecting fusion to the previously deposited layer of flowable material. The deposition process may be repeated so that successive layers of flowable material are deposited upon an existing layer to build up and manufacture a desired component structure. When executed properly, the new layer of flowable material may be deposited at a temperature sufficient to allow the new layer of such material to melt and fuse with a previously deposited layer in order to produce a solid part.
In some instances, the process of 3D printing a part may involve a two-step process. For example, the process may utilize a large print bead to achieve an accurate final size and shape. This two-step process, commonly referred to as near-net-shape, may begin by printing a part to a size slightly larger than needed, then machining, milling, or routing the part to the final size and shape. The additional time required to trim the part to a final size may be compensated for by the faster printing process.
There are two fundamental requirements for a compression roller to function properly when flowable material is pressed down or otherwise flattened to some extent, and leveled to a consistent thickness. First, the compression roller preferably rotates freely with little or no rotational friction or restriction to rotary motion. Friction in the rotation of the compression roller may exert an undesirable force on the melted bead during the print process, possibly distorting the print geometry. Second, the compression roller preferably remains at a temperature that is below the melting temperature of the material being processed. This may be especially important when processing certain high temperature polymers such as, for example, polyphenylene sulfide (PPS), which may have an affinity for, and chemical attraction to, hot metal. When the compression roller reaches a certain temperature, the polymer being processed may adhere to the compression roller. Such adhesion may result in the compression roller jamming and/or the part being printed to sustain serious enough defects to render it unusable.
Early efforts to cool a compression roller may blow cooled air on the compression roller in an effort to remove enough heat to keep the temperature below the melting temperature of the material being processed. While such an approach may achieve adequate results for certain polymers that may be processed at lower temperatures, such a stream of cooled air may impart undesirable effects. For example, such a stream of cooled air may result in cooling of the print nozzle. Cooling of the print nozzle may negatively affect the temperature of the print bead, which may result in print process problems. Additionally, blowing cooled air on the compression roller may not remove sufficient heat from the compression roller when processing higher temperature polymers. For example, PPS may be processed at temperatures of 650° F. or higher to prevent the roller temperature from rising to a level that promotes adhesion of the polymer to the compression roller and blowing cooled air on the compression roller may not adequately remove heat.